TiddlyFox is an extension for older versions of Firefox that allows standalone TiddlyWiki files to save their changes directly to the file system. TiddlyFox works on both desktop and smartphone versions of Firefox. See Saving with TiddlyFox or Saving with TiddlyFox on Android for detailed instructions.
TiddlyFox is now obsolete due to its incompatibility with the latest versions of Firefox - see TiddlyFox Apocalypse. There are many alternatives to TiddlyFox, but none that work in precisely the same way – see GettingStarted for details.
TiddlyFox can be downloaded from the Mozilla Addons site: